<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        var px=document.documentElement.clientWidth;
        var font=document.getElementsByTagName("html")[0].style.fontSize=px/3+"px";
    </script>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .zyc{
            width: 200px;
            height: 200px;
            background-color: #cc0000;
        }
    </style>
</head>
<body>
<div class="zyc"></div>
</body>
</html>